The present disclosure relates to inkjet recording apparatuses, that is, recording apparatuses that perform printing by ejecting ink from nozzles.
Printing apparatuses that use ink are known. Such a printing apparatus includes a recording head. The recording head includes a plurality of nozzles. Based on image data, ink is ejected from the recording head onto a sheet. During the assembly of the printing apparatus, the fitting position of the recording head can deviate from the ideal position. A deviation in the fitting position results in a deviation in the landing position of ink. This can result in a color displacement. A technology for coping with a deviation in the fitting position of a recording head is known, as will be described below.
Specifically, a known inkjet recording apparatus is configured as follows. A plurality of recording heads, each having a plurality of nozzles arrayed at predetermined intervals, are arranged in a staggered formation in the nozzle array direction. There is a joint portion where a plurality of nozzles arranged in respective end parts of adjacently arranged recording heads overlap in the direction perpendicular to the nozzle array direction. A plurality of recording head units are arranged in the direction perpendicular to the nozzle array direction. Input image data is converted into ejection image data for each recording head unit. While a recording medium is being conveyed, ink is ejected from the nozzles of the plurality of recording heads according to the ejection image data to form an image. Based on measurement image data for forming a predetermined measurement image at a pixel position determined beforehand for each recording head, the plurality of recording head units are each made to form the measurement image. Errors in image formation position among the recording head units as identified from the measurement images formed by the plurality of recording head units respectively are identified for each recording head. From the error identified for each recording head, a corrected position for the ejection image data is determined so as to correspond to each recording head. An image is inserted or deleted at the determined corrected position to correct the ejection image data. This configuration is aimed at reducing a color displacement resulting from fitting with a deviation in the nozzle array direction.
In an inkjet recording apparatus, a plurality of recording heads are often arranged in a staggered formation in the main scanning direction (nozzle array direction). A plurality of recording heads are combined into a line head for one color. This helps increase the width of printable sheets. Such line heads have recording heads located at different positions in the sub scanning direction (sheet conveying direction). On the other hand, for a given line, printing positions have to be aligned in the sub scanning direction. Accordingly, for a given line, the timing of ink ejection at a downstream-side recording head is delayed, by a wait time, from that at an upstream-side recording head. The wait time is determined beforehand. For example, the wait time is determined based on the time calculated by dividing the specification-stated (designed) distance from the upstream-side recording head to the downstream-side recording head by the specification-stated sheet conveying speed.
In an inkjet recording apparatus, the size of one pixel (one dot) is extremely small. It is difficult to fit a recording head at an ideal position with no deviation as large as one pixel. Thus, the fitting position of a recording head can deviate from the specification-stated position (ideal position) in the sub scanning direction. A deviation in the fitting position of a recording head in the sub scanning direction can, inconveniently, lead to degraded image quality. For example, a deviation in the landing position of ink in the sub scanning direction can lead to degraded image quality. For example, a deviation from the intended position can produce a color that does not originate from the original (color displacement). To correct a color displacement requires accurately recognizing the amount and the direction of deviation in printing position.
The conventionally known technology mentioned above addresses a deviation in the fitting position of a recording head in the nozzle array direction (main scanning direction); it does not cope with a deviation in the fitting position of a recording head in the sub scanning direction, and thus does not give a solution to the inconvenience mentioned above.